Isotopic geochemistry of acid thermal waters and volcanic gases from Zaō volcano in Japan

Kiyosu, Yasuhiro; Kurahashi, Makoto

doi:10.1016/0377-0273(84)90028-3

Cited by 18 publications

(1 citation statement)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Matsubaya et al (1973) and Sakai and Matsubaya (1977) suggested that this endmember water represents the isotopic composition of magma. Recently, many studies have observed similar isotopic sig natures (e.g., Mizutani, 1978;Kiyosu and Kurahashi, 1984;Viglino et al, 1985;Kusakabe and Matsubaya, 1986;Mizutani et al, 1986;Taran et al, 1991;Giggenbach, 1992;Shevenell and Goff, 1993;Chiodini et al, 1995), and this endmember water is now recognized as high-tem perature vapor associated with subduction-zone *Now at Geological Survey of Japan, Higashi 1-1-3, Tsukuba city, Ibaraki 305, Japan (Email: imiyagi@gsjrstn.gsj.go jp). **Now at Department of Earth and Planetary Sciences, Hokkaido University, N10, W8, Sapporo 060, Japan.…”

Section: Introductionmentioning

confidence: 99%

Change in D/H ratio, water content and color during dehydration of hornblende.

1998

View full text Add to dashboard Cite

The hydrogen isotopic composition of hornblende in volcanic rocks has potential to indicate processes such as degassing of a magma reservoir, as well as the origin of magmatic water. However, during eruption and high-temperature interaction with air, the isotope composition of hornblende can be altered. In order to establish criteria to select natural hornblende that preserves magmatic hydrogen isotopic ratios, hydrogen isotopic composition (SD), water contents, and colors of hornblendes were measured. A series of heating experiments on natural green hornblendes was conducted in air and under vacuum up to 1000°C. There observed a negative relationship between the intensity of redness (a*) and water content among heated hornblendes in air and under vacuum, as well as natural samples from several Quaternary volcanos in Japan. Heating hornblende results in a significant increase in SD value that can be explained by a Rayleigh distillation (simultaneous degassing without hydrogen isotopic exchange between the gas and the mineral) model involving degassing of both H20 and H2. According to the model, maximum fractionation occurs when hornblende dehydrates only by H2 degassing. Application of the model indicates that hornblendes in pumice fragments from Plinian eruptions are most representative of the SD of pre-eruptive magma. In contrast, the SD values of minerals from lava flows, lava domes, or even from thick pumice flow deposits may have suffered from 1) hydrogen isotopic fractionation by mineral dehydration, and/or 2) isotopic re equilibration with degassing magma during eruption stage and during cooling stage after the emplacement.

show abstract